The Milky Way’s Galactic bar can punch holes in stellar streams

Sarah Pearson (Columbia University) // December 11, 2017

Abstract: As clusters of stars orbit our own Milky Way, a gravitational tidal interaction unfolds and the clusters tear apart into distinct morphological and kinematic structures. From our understanding of gravity, the distribution and motion of these stellar structures enable us to work backwards in time and thereby study our Milky Way’s evolution. Palomar 5 (Pal 5) is an old globular cluster orbiting our Galaxy while disrupting into thin leading and trailing stellar arms. In this talk, I will show that a previous encounter between the Pal 5 stellar stream and the Milky Way’s Galactic bar has punched a hole in the stream which can explain why the leading arm of Pal 5 appears to be a lot shorter than the trailing arm. The discovery that the bar can punch holes in stellar streams has important implications for near-field cosmology as the Milky Way should be filled with dark matter subhalos of various sizes according to the cold dark matter paradigm. One proposed method to detect subhalos is to search for them through disturbances in the structure of stellar streams, as dark subhalos should create gaps if they pass through or close by stellar streams. My work implies that caution should be applied before interpreting stream gaps as evidence for dark matter subhalos. Additionally, I will demonstrate how the Galactic bar’s interaction with the Pal 5 stream provides an intriguing methodology for studying our Milky Way’s Galactic bar in more detail.